1. Field of the Invention
The present invention generally relates to medical devices and methods useful for human mitral valve function repair and/or reconstruction. In particular, the present invention relates to a medical device that can be used to treat mitral valve regurgitation by replacing the function of native heart valves.
2. Description of the Prior Art
The human heart has four chambers and four valves. The heart valves control the direction of blood flow. Fully-functional heart valves ensure proper blood circulation is maintained during cardiac cycle. Heart valve regurgitation, or leakage, occurs when the leaflets of the heart valve fail to come fully into contact (coapt) due to disease, such as congenital, torn chordae tendineae, lengthened chordae tendineae, enlarged left ventricle, damaged papillary muscles, damaged valve structures by infections, degenerative processes, calcification of the leaflets, stretching of the annulus, increased distance between the papillary muscles, etc. Regardless of the cause, the regurgitation interferes with heart function since it allows blood to flow back through the valve in the wrong direction. Depending on the degree of regurgitation, this backflow can become a self-destructive influence on not only the function, but also on the cardiac geometry. Alternatively, abnormal cardiac geometry can also be a cause of regurgitation, and the two processes may “cooperate” to accelerate abnormal cardiac function. The direct consequence of the heart regurgitation is the reduction of forward cardiac output. Depending on the severity of the leakage, the effectiveness of the heart to pump adequate blood flow into other parts of the body can be compromised.
The mitral valve is a dual-flap (bi-leaflet) valve in the heart that lies between the left atrium (LA) and the left ventricle (LV). During diastole, a normally-functioning mitral valve opens as a result of increased pressure from the left atrium as it fills with blood (preloading). As atrial pressure increases above that of the left ventricle, the mitral valve opens, facilitating the passive flow of blood into the left ventricle. Diastole ends with atrial contraction, which ejects the remainder of blood that is transferred from the left atrium to the left ventricle. The mitral valve closes at the end of atrial contraction to prevent a reversal of blood flow from left ventricle to left atrium. The human mitral valve is typically 4-6 cm2 in opening area. There are two leaflets, the anterior leaflet and posterior leaflet, which cover the opening of the mitral valve. The opening of the mitral valve is surrounded by a fibrous ring called the mitral valve annulus. The two leaflets are attached circumferentially to the mitral valve annulus and can open and close by hinging from the annulus during cardiac cycle. In a normally-functioning mitral valve, the leaflets are connected to the papillary muscles in the left ventricle by chordae tendineae. When the left ventricle contracts, the intraventricular pressure forces the mitral valve to close, while chordae tendineae keep the two leaflets coapting (to prevent two valve leaflets from prolapsing into the left atrium and creating mitral regurgitation) and prevent the valve from opening in the wrong direction (thereby preventing blood from flowing back into the left atrium).
Currently, the standard heart valve regurgitation treatment options include surgical repair/treatment and endovascular clipping. The standard surgical repair or replacement procedure requires open-heart surgery, use of cardio-pulmonary bypass, and stoppage of the heart. Because of the invasive nature of the surgical procedure, risks of death, stroke, bleeding, respiratory problems, renal problems, and other complications are significant enough to exclude many patients from surgical treatment.
In recent years, endovascular clipping techniques have been developed by several device companies. In this approach, an implantable clip made from biocompatible materials is inserted into the heart valve between the two leaflets to clip the middle portion of the two leaflets (mainly A2 and P2 lealfets) together to prevent the prolapse of the leaflets. However, some shortcomings, such as difficulty of positioning, difficulty of removal once implanted incorrectly, recurrence of heart valve regurgitation, the need for multiple clips in one procedure, strict patient selection, etc., have been uncovered in the practical application of endovascular clipping.
In conclusion, there is a great need for developing a novel medical device to treat mitral regurgitation. None of the existing medical devices to date address this need fully. The present invention aims to provide physicians with a device and a method which can avoid a traumatic surgical procedure, and instead provide a medical device that can be implanted through a catheter-based, less invasive procedure for mitral regurgitation treatment.